Merging r341512:

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r341512 | ctopper | 2018-09-06 04:03:14 +0200 (Thu, 06 Sep 2018) | 7 lines

[X86][Assembler] Allow %eip as a register in 32-bit mode for .cfi directives.

This basically reverts a change made in r336217, but improves the text of the error message for not allowing IP-relative addressing in 32-bit mode.

Fixes PR38826.

Patch by Iain Sandoe.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@341530 91177308-0d34-0410-b5e6-96231b3b80d8